Auscultation apparatus

ABSTRACT

An electronic stethoscope including a microphone, amplifying equipment, and a loudspeaker for the user, also comprises an adjustable filter circuit. The filter circuit has a bandpass effect, and the center frequency and bandwidth of the passband can be adjusted at will throughout the audible range by the user.

The present invention relates to an ascultation apparatus, i.e. anapparatus for listening to sounds from the internal organs of a livingbody, preferably the heart, respiratory or circulatory organs of ahuman, in particular to be able to analyse the sound in a more detailedmanner for diagnostic purposes. The apparatus is intended to increasethe possibilities for correct diagnosis for e.g. a doctor, by providingmore detailed and specific sound information than what is possible whenusing e.g. an ordinary stethoscope, and the apparatus also providesoptions for recording, processing and displaying differentcharacteristics of the captured sound.

Various types of “electronic stethoscopes” are previously known: Frominternational No. WO 87/00145 (=SE 452,946) is known a means formonitoring respiration of infants, with microphones attached to the neckof the child. Each microphone is followed by a preamplifier, a bandpassfilter and further amplifying and signal processing equipment. However,a real loudspeaker device for listening to the sound is not included,instead there are various types of warning equipment for giving a signalif a certain type of sound does not appear for a certain period of time.The function of the bandpass filter is to remove irrelevant frequencies,and the relevant and permanently set pass range is 300-1000 Hz whenrespiratory sounds from a small child are monitored. Thus, thispreviously known device is specially designed for one signal function,and it cannot be used in the type of comprehensive analysis which is thegoal of the present invention.

From U.S. Pat. No. 4,220,160 is known an electronic stethoscopeincluding a microphone and amplifying and processing equipment whichlead to a loudspeaker for listening to processed sounds, as well as toother recording equipment. This is a system for transposing orconverting the sound in such a manner that e.g. very low frequencies(25-75 Hz) are shifted to frequencies above 250 Hz, which frequenciesare more easily audible and also easier to transmit e.g. by telephone.An adjustable highpass filter is inserted right after a microphonepreamplifier, in order to remove the very lowest frequencies (adjustablelimiting frequency in the range 0,5-20 Hz). Thus, the sound frequenciesreproduced in this case are shifted, and must be re-interpreted by thelistener.

From U.S. Pat. No. 4,731,849 is known an electronic stethoscope having amicrophone, a preamplifier, automatic gain control and bandpassfiltering before end amplification to a head set/loudspeaker. In thiscase the bandpass filter section comprises ten parallel bandpassfilters, however, all these filters operate simultaneously to transmitten selected/pre-set frequency ranges with about the same bandwidth. Theoutput from each filter can be attenuated to zero according to wish, sothat one has available ten fixed, selectable ranges which can be usedseparately or in combination. Thus, this arrangement provides certainoptions regarding choice of listening range, but is nevertheless arestricted system in this regard. The bandwidth is permanent for eachrespective one of the filters.

About the same options for varying the listening frequency range isprovided in German Offenlegungsschrift DE 41 00 607, which publicationalso exhibits an electronic stethoscope having various filters which canbe switched in and have different filter characteristics, inter aliabandpass characteristics.

However, none of the previously known devices seem to give to the doctorwho shall prepare the diagnosis, complete and free options for selectingwhich frequency range shall be used, i.e. possibilities for decidingfreely and immediately which part of the sound spectrum should form thebasis of the analysis, without regard to whether the sound shall belistened to or recorded in some other manner.

The present invention has been conceived just to provide suchpossibilities, and this is achieved in accordance with the invention byproviding an apparatus of the type as defined in patent claim 1.

Further embodiments of the invention are defined in the attacheddependent patent claims.

The invention will be described in closer detail in the following, withillumination of exemplary embodiments and with reference to the appendeddrawings, where

FIG. 1 is a block diagram showing an embodiment of the invention whichincludes an automatic gain control unit,

FIG. 2 shows an embodiment including equipment for digital processing ofthe sound signals, in the form of a block diagram, and

FIG. 3 is a more detailed block diagram showing an exemplary embodimentof the apparatus of the invention.

In FIG. 1 appears in a block diagram a relatively simple version of anapparatus in accordance with the invention. The microphone 1 is of atype which is suited to be attached to an appropriate place on a body,in regard to the type of body sound to be monitored. Various microphonetypes are of interest, however the microphone type itself does notconstitute any part of the present invention. The signals captured bythe microphone 1 pass to a microphone preamplifier 2 which either may bebuilt together with a microphone in order to shorten the conductor pathbetween microphone and preamplifier, with regard to the fact that theweak signals are to a large degree exposed to degradation from noise, orthe preamplifier 2 can be physically built together with the unitsfollowing thereafter. In many applications it may be sensible to includean automatic gain control unit 3 after the preamplifier to ensure anuniform level of the sound to be analysed. However, such a unit is notabsolutely necessary for the invention.

The central feature of the present invention is to be found inconnection with the adjustable filter circuit shown with referencenumeral 4. The special characteristics of the filter circuit 4 shall bementioned later. However, the filter circuit 4 is arranged to transmit acertain frequency band, most often within the audible range 20 Hz-20kHz, but it may also be of interest to make an analysis in an extendedsound frequency range beyond the ordinary 20 kHz limit, and also down inthe infrasound range below 20 Hz. This filtered signal passes further onto a sound frequency amplifier 5 which is adapted to deliver power to aloudspeaker 6, or possibly a head set may be more appropriate (see FIG.3). All units 2-5, or possibly 1-5 if the microphone is of a type whichrequires a voltage supply, can be fed from a common power supply 7.

FIG. 2 shows an embodiment of the apparatus of the invention, which issomewhat different. The differences existing with regard to FIG. 1, arefirst that the automatic gain control unit 3 has been left out, whichhas been previously stated as a possibility, and next that an equipment8 for analog/digital conversion of the signals from the preamplifier hasbeen added, possibly for conversion of signals from the main amplifier5, i.e. after execution of filtering. The sampled and digitized signaldelivered by the converter 8 is passed to a digital processing equipment9, and it is of course possible to include herein digital filters whichare able to conduct the same type of filtering as basically executed incircuit 4. For the rest, the circuit is of the same type as shown inFIG. 1.

FIG. 3 shows, still in the form of a block diagram, a more detailedrepresentation of a circuit which is a combination of the versions shownin FIG. 1 and FIG. 2. Both the automatic gain control unit 3 and thedigital equipment 8, 9 are included, and in addition an output circuit15 has been included, which output circuit is able to deliver a signalto a head set 16 or to auxiliary equipment 17 (a printer, a screendisplay apparatus or similar) which corresponds to the signal toloudspeaker 6. In order to switch at will concerning digitizing theoriginal signal from preamplifier 2, or digitizing the filtered signalfrom the main amplifier 5, a switch 18 has been inserted. However, themost important features in the drawing are the units in closeassociation with the adjustable filter circuit 4:

The filter circuit 4 is a bandpass filter wherein both center frequencyand bandwidth for the passband shall be adjustable, freely and asdesired. A Q factor module 14 takes care of the bandwidth, and thismodule may be of a type having permanent Q factor values to be selectedby means of a switch, or this Q factor module may be of a type having aninfinitely variable regulator function, so that any bandwidth can bechosen. The adjustable filter circuit 4 is of a type where the passbandcenter frequency can be adjusted by means of a supplied externalfrequency. This frequency is supplied from an oscillator 11, and theoscillator frequency is governed by means of a frequency module 10 whichsets a number of main frequencies for the oscillator 11. Furthervariation of the oscillator frequency is achieved by means of aninfinitely variable adjustment of a potentiometer (not shown) connectedto the oscillator 11.

It will be favourable if the doctor is able to see both the centerfrequency and the bandwidth used for the moment, and it will thereforebe favourable to arrange a display 12 in connection with the filtercircuit 4. The display 12 is run by a unit 13 which controls thefrequency and drives the display.

Thus, the advantage of the apparatus in accordance with the invention isthat the user himself is able to decide exactly which frequencies withinthe audible picture he desires to listen to by adjusting the centerfrequency and bandwidth of the bandpass filter. In combination withamplification of the signal from the microphone before and afterfiltering, it is achieved that it is possible for the user to obtain asound picture from the loudspeaker which is very rich in detail and verygood. It is to be noted that the technology of adjusting frequency andretrieving a certain frequency band for investigating this bandseparately, in itself is no novelty, since a similar technique has beenused previously e.g. within the field of radio technology. But when usedin an auscultation apparatus, it is a novelty that the user, e.g. thedoctor, has complete control over what part of the audible spectrum canbe used in the analysis/diagnosis.

In this connection it is to be understood that a typical sound frequencyrange for the so called first and second heart sounds is in the range20-150 Hz, while respiratory sounds are in the range 200-750 Hz,mitral/aortic blood regurgitation is heard in the range 170-900 Hz,mitral stenosis can be heard in the range 25-80 Hz, etc. Thus, whenlistening for a certain phenomenon, it will be very favourable to beable to remove irrelevant frequencies, and it is clear that the presentinvention provides new such possibilites.

What is claimed is:
 1. Auscultation apparatus, comprising a microphonefor direct contact with a body surface, an adjustable electronicbandpass filter circuit connected after the microphone, said filtercircuit having a passband center frequency that can be adjusted by meansof an externally supplied frequency, and listening/monitoring equipmentincluding a sound frequency amplifier and loudspeaker means forreproduction of the filtered sound, wherein the center frequency as wellas bandwidth of the filter passband are independently adjustable wherean adjustment of either does not affect the other at least throughout afrequency range of from 20 Hz to 20000 Hz by means of a Q-factor modulefor controlling bandwidth and a frequency module and an oscillator forthe controlling center frequency, said oscillator and said Q-factormodule being connected directly and mutually independently to saidfilter circuit.
 2. Auscultation apparatus in accordance with claim 1,wherein the self-contained microphone unit further includes an automaticgain control unit connected to the preamplifier for variableamplification of the signal from the microphone.
 3. Auscultationapparatus in accordance with claim 1, or 2, wherein frequency ranges arefixed and center frequency and bandwidth are freely adjustable withineach respective range.
 4. Auscultation apparatus in accordance withclaim 1, or 2, including a quick selector switch for easy selection ofbandpass ranges with pre-adjusted center frequencies and Q factors. 5.Auscultation apparatus in accordance with claim 1 or 2, including aninfinitely variable regulator connected to the bandpass filter foradjusting Q factor and hence the bandwidth of the passband. 6.Auscultation apparatus in accordance with claim 1 or 2, wherein thebandpass filter includes a display for showing set values of centerfrequency and bandwidth.
 7. Auscultation apparatus in accordance withclaim 1 or 2, including a digitizing means for digitizing the signalsfrom the microphone for digital processing.
 8. Auscultation apparatus inaccordance with claim 1, further comprising a memory means for recordingand storing the filtered sound.
 9. Auscultation apparatus in accordancewith claim 2, further comprising a listening/monitoring equipmentcomprising a sound frequency amplifier and loudspeaker means forreproduction of the filtered sound.
 10. Auscultation apparatus inaccordance with claim 2, further comprising a processing means forextracting predefined characteristics of the filtered sound.